1. Field of the Invention
The present invention concerns a die molding apparatus for molding resin articles. The molding apparatus has a plurality of molds for defining a cavity including a main cavity portion extending substantially linearly in a mold closure state one end thereof being in communication with an injection gate, and has a gas charging nozzle capable of charging at least the inside of the main cavity portion with a gas from the one end after injection of a predetermined amount of molten resin from the injection gate has been completed. The apparatus is used to form a resin article including a main portion an outer shape conforming the shape of the main cavity portion and having a hollow inside having a shape corresponding to that of the cavity by the charging of the gas.
2. Statement of Related Art
In such molding apparatus described above, a resin article having a hollow portion at least in the inside of the main portion of article has been molded by charging a gas at least to the inside of the main cavity portion from one end thereof after injection of molten resin from an injection gate. However, since the other end of the main cavity portion is closed and there is no room for relieving the molten resin upon charging of the gas, wall thickness is increased locally at the other end of the main portion of the resin article after the completion of molding, which sometimes results in mold sink marks and degrades the commercial worth of articles.
For preventing such sink marks in existent resin molding, it has been provided a molding apparatus in which an excess molten resin from the main cavity portion is relieved to an overflow portion in communication with the other end of the main cavity portion. Then, it is possible to prevent localized increase of the wall thickness at the other end of the main portion of the resin article. However, since the gas is also relieved partially to the overflow portion, when the excess part of the resin corresponding to the overflow portion is removed from the completed molding resin article, a through hole is formed undesirably at the other end of the main cavity portion due to the partial escape of the gas into the overflow portion. This necessitates a treatment for closing the through hole. As a result, it takes an additional labor corresponding to this treatment and, in addition, the aesthetic appearance after closing the through hole is degraded.
Further, in the die molding apparatus of the aforementioned type, the gas charging nozzle is arranged such that the surface at the top end thereof is flush with the inner surface of the cavity and the gas is charged to the inside of the cavity from the gas charging hole provided at the inner end of a tapered recess open to the top end.
However, in the gas charging nozzle of the arrangement described above, the gas tends to leak from the top end of the gas charging nozzle to often result in defective articles. In addition, although a ball member is provided at the gas charging hole for preventing the molten resin from flowing back from the gas charging hole into the gas charging nozzle, the molten resin reaches the gas charging hole along the inner surface of the recess and the ball is caught and fixed by the molten resin to often clog the gas charging hole.
Furthermore, in the existent molding apparatus, a molten resin reaches the gas charging hole along the inner surface of the recess to form a tapered hollow cylindrical portion integrally at one end of the completed molding resin article. Then, the hole or opening at the outer end of the hollow cylinder has to be sealed after the completion of resin molding process (hereinafter, the hollow cylinder portion is referred to as a hole-sealed hollow cylinder). However, since the thickness of the molten resin flowing along the inner surface of the recess is very small, the gas tends to leak through the wall portion of the hole-sealed hollow cylinder. This sometimes results in defective articles. Further, since the hole-sealed hollow cylinder can not always be formed into a definite identical shape, it sometimes makes the sealing treatment for closing the opening at the outer end of the hole-sealed hollow cylinder troublesome.
A first object of the present invention is to overcome such drawbacks and to provide a die molding apparatus for molding a resin article, capable of saving additional subsequent finishing treatment and giving excellent aesthetic appearance for the resin article.
A second object of the present invention is to provide a die molding apparatus for molding a resin article, capable of preventing the leakage of a gas to be charged from a gas charging nozzle into a cavity and also capable of preventing a gas charging hole from being clogged.
A third object of the present invention is to provide a die molding apparatus for molding a resin article, capable of avoiding the leakage of a gas charged from a gas charging nozzle in a cavity and capable of stabilizing the shape of a hole-sealed hollow cylinder, thereby facilitating subsequent sealing treatment.
In accordance with the first aspect of the present invention, the foregoing first object can be attained by a die molding apparatus for molding resin articles,
the apparatus having a plurality of molds for forming a cavity including a main cavity portion extending substantially linearly in a mold closure state one end thereof being in communication with an injection gate, and a gas charging nozzle capable of charging at least the inside of the main cavity portion with a gas from the one end after injection of a predetermined amount of molten resin from the injection gate has been completed, and
the apparatus being used to form a resin article including a main portion having to a shape conforming the shape of the main cavity portion and having a hollow inside formed by the charging of the gas to a shape corresponding to the shape of the cavity, wherein
an overflow portion for relieving an excess molten resin from the main cavity portion and a film gate for communication between the other end of the main cavity portion and the overflow portion are formed between a pair of molds that define the other end of the main cavity portion, and
the gap between the pair of the molds is set to 1.5 mm or less at a part corresponding to the film gate.
According to the constitution described above, since the excess molten resin in the main cavity portion is relieved from the other end of the main cavity portion to the overflow portion, localized increase of the wall thickness at the other end of the main portion of the molded resin article can be prevented thereby enabling to prevent sink marks after the completion of molding, which worsened the commercial worth of the article so far.
Particularly, the other end of the main cavity portion and the overflow portion are connected by way of the film gate, and it has been confirmed experimentally by the present inventors that the gas is not relieved from the film gate to the overflow portion providing that the gap between both of the molds is 1.5 mm or less at a part corresponding to the film gate.
Accordingly, when the end of the film gate on the side of the main cavity portion is cut off from the resin article after the completion of the molding resin article so as to remove the excess portion corresponding to the film gate and the overflow portion, a through hole which was formed undesirably by the gas, is no more present at the other end of the main portion of the article. Thus, a subsequent treatment for closing such through hole is not necessary, to save additional labors and, accordingly, aesthetic appearance after the cutting is not deteriorated.
Further, in a modified embodiment of the first aspect of the present invention described above, the molds are adapted such that the resin article integrally comprises a main portion of article having a decorative surface on one surface and a projection projecting from the other end of the main portion of article on the side opposite to the decorative surface, and the overflow portion and the film gate are formed between a mold fir forming the decorative surface of the main portion of article, and another mold for forming a lightening portion open to the other end of the main portion of article.
In this modified constitution, the gap between the mold for forming the lightening portion and the mold for forming the decorative surface of the main portion of article can be narrowed to restrict the flowing area of the gas at the upstream of the film gate along the flowing direction of the molten resin and the gas at the other end of the main cavity portion, so that the flow of the gas from the film gate to the overflow portion can be shut off more effectively. Furthermore, since a projection projecting on the side opposite to the decorative surface is disposed integrally and in contiguous with the other end of the main portion of article having the decorative surface on one surface, the wall-thickness at the other end of the main portion is not reduced excessively by the formation of the lightening portion.
In accordance with a second aspect of the present invention, the foregoing second object can be attained by a die mold molding apparatus for a resin article,
the molding apparatus having has a plurality of molds for defining a cavity in communication with an injection gate in a mold closure state, and a gas charging nozzle capable of charging the inside of the cavity with a gas after injection of a predetermined amount of molten resin from the injection gate has been completed, and
the molding apparatus being used to mold a resin article having a hollow inside formed by charging of the gas to a shape conforming the shape of the cavity, wherein
the gas charging nozzle is situated in the cavity such that a gas charging hole provided at a top end of the nozzle is arranged at a position corresponding to the hollow inside of the resin article.
According to the constitution described above, since the gas charging nozzle having the gas charging hole at the top end situates in the cavity such that the gas charging hole is arranged at a position corresponding to the hollow inside formed in the resin article, the top end of the gas charging nozzle penetrates the shell wall of the resin article that defines the hollow inside and the wall thickness of the molten resin at the periphery of the top end of the gas charging nozzle is increased to minimize the leakage of the gas and reduce the worry of resulting in defective articles. In addition, since the gas charging hole is exposed to the charging gas, it is also possible to prevent clogging of the gas charging hole.
In accordance with the third aspect of the present invention, the foregoing object can be attained by a die mold molding apparatus for a resin article,
the molding apparatus having a plurality of molds for forming a cavity in communication with an injection gate in a mold closure state, and a gas charging nozzle capable of charging the inside of the cavity with a gas after injection of a predetermined amount of molten resin from the injection gate has been completed, and
the molding apparatus being used to mold a resin article having a hollow inside formed by charging of the gas to a shape conforming the shape of the cavity, wherein
an insertion hole in communication with the inside of the cavity is provided in one of molds that corresponds to one end of the cavity;
the gas charging nozzle to be inserted into the insertion hole has a cylindrical large diameter portion fitted in the insertion hole and a cylindrical small diameter portion coaxially contiguous with the top end of the cylindrical large diameter portion while forming a circular step facing the cavity between the large diameter portion and the small diameter portion, and
a hole-sealed hollow cylinder which integrally projects from the resin article and which is to be subjected to a hole sealing treatment after completion of molding of the resin article is formed between one of the molds that corresponds to one end of the cavity and the gas charging nozzle, the hole-sealed hollow cylinder having an inner surface shape defined by the outer surface of the cylindrical small diameter portion and the step portion and an outer surface shape defined by the inner surface of the insertion hole provided in the cavity.
In accordance with the constitution described above, since the hole-sealed hollow cylinder having the inner surface shape defined by the outer surface of the cylindrical small diameter portion and by the step portion and the outer surface shape defined by the inner surface of the insertion hole provided in the cavity is formed being integrally projected from the molding resin article by the charging of the gas after injection of the molten resin, the wall-thickness of the hole-sealed hollow cylinder can be increased to minimize the leakage of the gas thereby enabling to reduce the worry of resulting in defective articles and, further, it is possible to form the hole-sealed hollow cylinder always in an identical definite shape thereby facilitating the subsequent sealing treatment for the opening or hole at the outer end of the hole-sealed hollow cylinder.